I found this on Vinted, it's for the Atari 2600, and from what I can find out there was only one game released that took advantage of it, Star Raiders, which was included with the controller
You get twelve buttons in a rectangle shaped handheld
It has rubber feet and plugs into the normal controller port
Game specific overlays could be used
The Star Raiders game with instructions and keypad overlay
?TYPE MISMATCH ERROR